Technically, it would be possible, but I'm not sure about the design implementation. Would you want to be able to add "multiple" images into Tinymce? There is no pre-designed interface in Files gallery for "selecting" an image or multiple images, and "insert" into another app like Tinymce.
How it can be achieved technically:
- Open Files gallery in some popup or modal window.
- Simple function for
click on the custom context menu, to postMessage() to the Tinymce app window, and simply close itself (window).
Quite straight-forward to achieve, but as noted, there is no pre-designed interface in Files gallery for this.